The department of oral surgery in Ghent has a lot of patients for bilateral sinus lift procedures. The group of patients should have enough bone for installation of 4 dental implants in the area 14-24. In this region 4 implants will be installed and immediate loading with a provisional acrylic (metal reinforced) bridge will be provided. The survival and success of the implants immediate functional loading will be studied (interest point 1). Two different implant surfaces are used in the study to be compared (interest point 2) in relation to peri-implant parameters, radiographical healing, and success criteria at the same time bilateral sinus lifting is performed. One sinus is filled with a mixture of iliac crest bone and Bio-Oss (Geistlich Germany), and the second sinus is filled with calvarial skull bone and Bio-oss. The latter bone combination is appreciated clinically by the surgeons since it leads to a subjectively better implant stability. This, however, remains to be investigated. This study can compare both harvesting techniques and evaluate clinical treatment outcome (interest point 3). Normally, there is a certain waiting time after sinus lifting before dental implants are installed. Recently, however, some literature abstracts indicate that immediate placement of the implants in the sinus lifted bone can be successful. However, this is not done with immediate functional loading. We propose to install in total 6 miniscrews, 2 in each sinus lift area. Four will be loaded immediately and connected rigidly to the other 4 normal sized implants. Actually the immediate loaded bridge will be supported, in total, by 4 normal and 4 miniscrew implants. Four months after loading, the 4 loaded miniscrews are removed with a trephine drill in order to examine soft-tissue healing, bone-implant contact, and bone healing by means of histomorphometry. Since the implants are in cortical bone + sinus lifted bone, it will be possible to examine the given implant surface under immediate loading in both bone conditions (interest point 4). Immediately after removing the miniscrews, they are replaced by the normal sized implants. One side will be randomly assigned for immediate non-functional loading, the other side will be assigned to a non-loaded condition. With this latter design we can mimic the partial sinus lift condition as it is often done 4 months after sinus lifting - the classical procedure. At the time of exposing the implants of the 2-stage procedure, the miniscrews are removed. This gives us an idea of bone healing of an implant installed 4 months after sinus lifting and kept additionally unloaded for 4 months. This gives us histology of immediately loaded implants in healed sinus lifted bone (interest point 5).